312 HISTOLOGY OF THE MORBID PROCESSES. 



action. Toward the periphery of the inflammatory focus these 

 poisons are more dilute, and exert a positive chemotactic influ- 

 ence upon the leucocytes, stimulating their emigration and prog- 

 ress toward the centre of the inflamed area. If they advance 

 too far, however, or the accumulating poisons become too con- 

 centrated, they suffer necrosis or degeneration in the same manner 

 as the tissues of the part. In this way the necrotic process may 

 advance more rapidly than the restricting inflammatory process can 

 cope with it. But to a certain extent the poisons they produce are 

 injurious to the bacteria themselves, so that as they become more 

 concentrated the growth of the bacteria is checked. The injurious 

 influence of the bacteria upon the tissues is also, after a time, miti- 

 gated by the production within the body of chemical substances 

 called " antitoxins," which neutralize the poisons produced by 

 the bacteria. Other substances may also be produced which 

 have a germicidal action. There will come a time, therefore, pro- 

 vided the individual lives, when the productive inflammatory process 

 on the part of the tissues will predominate over the destructive 

 action of the bacteria and confine the poisonous area within a zone 

 of granulation-tissue. This demarcation does not take place in most 

 cases until a collection of pus, an abscess, has been formed in and 

 around the area of necrosis. The appearances are then different, 

 and require a brief description. 



An abscess or collection of pus within the tissues contains a fluid 

 of serous character, in which there is such a great number of sus- 

 pended leucocytes that they give it a milky or creamy appearance. 

 This liquid is pus (Figs. 275, 276, and 292). The walls enclosing 

 the pus are composed of granulation-tissue infiltrated with emi- 

 grated leucocytes making their way to the fluid contents. The 

 liquefaction of the tissues which makes the central cavity pos- 

 sible is the result of maceration, the disintegrating action of the 

 leucocytes, and, probably in still greater degree, is due to a pep- 

 tonizing action exerted by the bacteria or their products. There 

 is now an antagonistic action between the bacteria and their 

 products and the tissues, in which possibly the phagocytic action 

 of the leucocytes may aid the tissues. The activities of the tis- 

 sues are directed to the formation of cicatricial tissue ; the bac- 

 teria and their products tend to impede those activities or to 

 destroy their results. If the destructive action predominates, the 

 pus increases in amount and a burrows," following the direction of 



